Aspirin, the ubiquitous pain reliever, goes by the chemical name acetylsalicylic acid. One of the compounds used in the synthesis of aspirin is salicylic acid, which is itself a pain reliever that was known to many ancient cultures, including the Native Americans who extracted it from willow tree bark. Salicylic acid is extremely bitter tasting, and frequent use can cause severe stomach irritation. The search for a milder form of this pain reliever led to the successful synthesis of acetylsalicylic acid by the German chemist Felix Hoffmann in 1893.

Your two primary objectives in this experiment will be to synthesize and analyze aspirin. There is more than one way to synthesize aspirin; in this experiment, you will react acetic anhydride with salicylic acid in the presence of phosphoric acid (which acts as a catalyst). The reaction equation is shown below.

{\left( {{\text{C}}{{\text{H}}_{\text{3}}}{\text{CO}}} \right)_{\text{2}}}{\text{O }} + {\text{ HO}}{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{4}}}{\text{COOH }} \to {\text{ C}}{{\text{H}}_{\text{3}}}{\text{C}}{{\text{O}}_{\text{2}}}{{\text{C}}_{\text{6}}}{{\text{H}}_{\text{4}}}{\text{C}}{{\text{O}}_{\text{2}}}{\text{H }} + {\text{ C}}{{\text{H}}_{\text{3}}}{\text{COOH}} Acetic{\text{ }}anhydride{\text{ }} + {\text{ }}salicylic{\text{ }}acid \to acetylsalicylic{\text{ }}acid + acetic{\text{ }}acid

You will conduct two tests of your synthesis to verify that you did indeed make aspirin, and to determine its relative purity. First, you will measure the melting point of a sample of your product. Second, you will use a Colorimeter or Spectrometer to test the absorbance of your aspirin after it has been “prepped” with an iron solution to give it color.


In this experiment, you will

  • Synthesize a sample of acetylsalicylic acid (aspirin).
  • Calculate the percent yield of your synthesis.
  • Measure the melting temperature of your aspirin sample.
  • Conduct a colorimetric analysis of your aspirin sample.